The T-lymphotropic retrovirus family includes among other lentiviruses the simian retrovirus SIV and the human retroviruses HIV-1 (the likely etiologic agent of AIDS) and HIV-2. Although HIV-1 and HIV-2 are related evolutionally, nucleic acid sequence analysis reveals that HIV-2 is more closely related to SIV than it is to HIV-1. Guyader et al. (1987) noted only 42% overall genomic sequence identity between the HIV-1 and HIV-2 isolates they compared. Patients infected with HIV-2 can manifest disorders that typify AIDS, purely neurologic disease or asymptomatic infections (Kuhnel et al., 1988) despite HIV-1-related ultrastructural and biological properties such as in vitro cytopathogenicity and CD4 tropism (Clavel et al., 1986).
The HIV-1 and HIV-2 genomes have a typical retroviral configuration comprising LTR's, gag and env regions that encode viral structural proteins, sequences encoding one or more enzyme, including a reverse transcriptase and other ORF's and regulatory elements. The gag region of HIV-1 encodes a precursor peptide known as p55. p55 is processed to produce among other proteins the major core or capsid protein known as p24. In HIV-2, the analogous E precursor is larger, known as p57, and the major core protein is known as p26. Although a high degree of conservation of the gag proteins of HIV-1 and HIV-2 was expected, Guyader et al. (1987) found only 58% identity of amino acids between HIV-1 and HIV-2 gag proteins. Even among distant isolates of HIV-1 there is a greater than 90% identity of gag proteins. That and other data support the hypothesis that although HIV-1 and HIV-2 are somewhat related, they are nevertheless distinct retroviral species.
Because HIV-1 and possibly HIV-2 have such an impact on the human immune system, it is desirable, in fact imperative that sensitive, rapid diagnostic assays for detecting presence of HIV be available for population screening, quality control in blood banks, diagnosis, furtherance of our understanding of those viruses to assure the goal of obtaining a vaccine and cure, and the like. Because of ease and convenience, it is preferable that the assays be immunology-based, such as ELISA's, and for reproducibility, specificity and consistency that the reagents be monoclonal antibodies and defined antigenic peptides. Because p24 antigenemia has been shown to be an early sign of HIV infection (Kessler et al., 1987; Wall et al., 1987) and the observation that clinical progression of AIDS sequelae is associated with reduction in anti-p24 while patients with AIDS can die with high levels of anti-env titers (Coates et al., 1987), it would be advantageous for the assay to be directed to detecting gag products such as p24/p26.
Weiss et al. (1988) identified human serum samples that contained antibodies specific to HIV-2 gp130 in radioimmunoprecipitation assays and in ELISA's. Those antibodies showed low level HIV-1 crossreactivity in a VSV pseudotype neutralization assay and in a neutralization of C8166 syncytia formation assay.
Minassian et al. described a monoclonal antibody identified as R1C7 that was raised against HIV-2. R1C7, an anti-capsid antibody (p26), reacted not only with the three HIV-2 isolates tested, but with the five HIV-1 isolates and seven SIV isolates that were tested. In immunoblots, R1C7 bound to 55KD and 26KD HIV-2 proteins, to 24KD and 55KD HIV-1 proteins and to a 28KD SIV protein.
Niedrig et al. developed a panel of 29 monoclonal antibodies to HIV-1. One antibody was directed to p17 and its precursor p32 whereas the remainder reacted with p24 and some of those also reacted with p55. The p17 antibody was found to be HIV-1 specific. Of the 28 anti-p24 antibodies, 20 reacted in immunoblots with the corresponding capsid protein (p26) of HIV-2 and five of those also recognized the corresponding SIV protein, p28. Niedrig et al. make no mention of antibody titer, the efficacy of the antibodies in a antigen capture assay or which of the antibodies bind to p26, p55 or both. Furthermore, several of antibodies reacted with a 22KD protein of unknown function in HIV-2 preparations.
Many diagnostic kits and assays have been developed for the detection of HIV-1 in samples of sera, blood, blood products or other body tissues. The assays use a variety of techniques such as Western blot, enzyme-linked immunosorbent assay (ELISA) or indirect immunofluorescent assay and employ either antibodies to whole virus or purified viral antigens, see for example, Gallo et al., U.S. Pat. No. 4,520,113; Sarngadharan, et al., (1984); and Robert-Guroff et al. (1982).